Project Summary/Abstract Nerve, heart and muscle cells require voltage-gated Ca2+ channels (VGCC) whose opening triggers neurotransmitter release and muscle contraction. VGCC opening may also trigger slower processes such as cell migration, gene transcription and apoptosis. Pharmacologically, these channels are currently targeted in chronic pain, hypertension and stroke. Mutations in these channels have been directly implicated in autism spectrum disorder, Alzheimer's disease, schizophrenia, epilepsy, migraine, atrial fibrillation, Brugada syndrome and several other neurological and cardiovascular disease. The immediate effect of some of these mutations is to alter channel gating in a way that severely changes channel inactivation, leading to aberrant Ca2+ influx into cells. For example, Timothy syndrome (TS) is characterized by autism or autism spectrum disorder and severe cardiomyopathy that leads to death by the age of 3 or 4. The abnormalities arise from a single point mutation that slows cardiac Ca2+ channel inactivation, resulting in an abnormally large Ca2+ influx. RGK proteins are small GTPases that dramatically inhibit Ca2+ channels. Strikingly, we have uncovered in our preliminary studies that TS mutants are insensitive to inhibition by low levels of RGK proteins, that otherwise strongly inhibit Wild Type (WT) channels. Furthermore, we found that slowed channel inactivation is what affords protection against RGKs. Correspondingly, we found that VGCC mutations that speed inactivation, such as those that cause familial hemiplegic migraine, turn channels hypersensitive to RGK inhibition. To explain these effects, we hypothesized that RGK proteins lock channels in the inactivated state. We also hypothesized that RGK-mediated inhibition can be modulated dynamically, by proteins or drugs that control Ca2+ channel inactivation. We will test these hypotheses in the current proposal. In addition, we will investigate whether RGKs differentially inhibit the surface expression of WT versus mutant channels. These and other emergent hypothesis will be investigated in frog oocytes, HEK293 cells, and cardiac myocyte HL-1 cells, using a combination electrophysiological, biochemical, imaging, and flow cytometry studies. Thus, our proposal reveals a new mechanism for RGK- mediated VGCC inhibition and investigates a new facet for calcium channelopathies. In addition, it will likely emerge that RGKs amplify the action of proteins and drugs that alter VGCC inactivation, which could have consequences for both health and disease.